Leaded brasses (alloys within the 300 series of the Copper Development Association standard designation) are quite useful for making parts on high speed automatic screw machines. These particular alloys are quite useful because of their very good machinability. This machinability is brought about principally by the addition of lead to the copper-zinc base in the alloy system. Unfortunately, these particular alloys are quite difficult to commercially process because of their inherent poor hot workability. It seems that the material exhibits a large number of edge cracks during hot working and particularly during hot rolling of the alloy into strip material. The incidence of edge cracking during the hot rolling procedure is usually quite severe and thus results in high material loss from the particular strip and subsequent high cost involved in producing the strip.
The leaded brasses, while being quite useful for machining operations, are not particularly noted for their strength properties. Various means have been studied to produce leaded brass alloys which maintain their good machinability characteristics but which also provide a larger amount of useful material when hot worked.
For example, a report entitled "Study on High Strength Free-Cutting Brass for Watch Parts" issued in the annual report of the Engineering Institute of Tokyo University, Volume 22, No. 1 (1963), on Pages 27 to 31 describes the addition of various other elements to a copper-zinc-lead alloy system to improve the strength of the system. This particular article discussed the addition of fourth and fifth elements to the three element based system and the addition of such elements as chromium in particular to such a system. It was found in the study described in the report that chromium moderately increased the strength of the base free-cutting brass alloy system. Various other elements such as titanium and manganese provided the alloy system with a larger increase in tensile strength. U.S. Pat. No. 2,046,088 has disclosed the addition of chromium to those alloys which contain copper, zinc and lead, wherein the lead is apparently limited to approximately 0.01%. This particular patent appears to be mainly concerned with producing improved welding rods which reduce the amount of noxious fumes when utilized in a welding apparatus. Nothing is taught in either reference which suggests the particular alloy system of the present invention.
It is, therefore, a principal object of the present invention to provide a leaded brass alloy system which exhibits increased resistance to edge cracking during hot working.
It is a further object of the present invention to provide such an alloy system which achieves these increases in strength and resistance to edge cracking while maintaining the good machinability characteristics of leaded brasses.
Further objects and advantages of the present invention will become more apparent from a consideration of the following specification.